An agricultural vehicle having a grille screen and a front end bumper is described herein. The bumper has a top surface and is disposed below the screen. The screen includes a plurality of convolutions having lower edges with open ends. Adjacent convolutions define intervening channels that provide a guided track on which impacting debris can move downwardly toward the lower edges to fall either on the ground or on the top surface of the bumper. The lower edges of the convolutions and the top surface of the bumpers are spaced apart by a gap sized to permit accumulated dirt and chaff to be wiped off the top surface of the bumper.